Delta-9-tetrahydrocannabinol and olivetol have been shown to induce errors of chromosome segregation in both normal human lymphocytes and human lymphoid cell line when added in vitro. These studies are leading to the development of a cytogenetic model for examination of environmental mutagens. Further studies are in progress to examine the effect of non-psychoactive cannabinoids on the segregation of chromosomes. Marihuana smoking has been shown to induce hypoploid cells with chromosome complement of less than 30 per nucleus. However, no increase in segregational errors of chromosomes was found in 5 subjects who smoked marihuana under a controlled environment. Attempts are being made to establish clonal cells with hypoploid complements. Possible mutagenic effects of THC are being studied in fertilized mice ova. Early gestational products from female mice exposed to THC are examined for their ability to synthesize macromolecules.